Path: utzoo!attcan!uunet!husc6!uwvax!vanvleck!uwmcsd1!ig!agate!ucbvax!ji.Berkeley.EDU!carlton
From: carlton@ji.Berkeley.EDU (Mike Carlton)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Transfer problems
Message-ID: <24772@ucbvax.BERKELEY.EDU>
Date: 20 Jun 88 08:06:50 GMT
References: <18251@sri-unix.SRI.COM>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: carlton@ji.Berkeley.EDU.UUCP (Mike Carlton)
Organization: University of California, Berkeley
Lines: 22

(Sorry to post this, email bounced)
In article <18251@sri-unix.SRI.COM> dbeck@unix.sri.com (Douglas K. Beck) writes:
>is to move 16 megabytes of data from a National Semi add in
>board in my Mac II to a parallel output port.  The task requires
>that a new long word be delivered in one microsecond or under.
...
>residing in the cache.  The execuition speed I obtain is 1.22us
>per longword transfer. Where did I go wrong?  A demoralized mind
>wants to know.
>dbeck@unix.sri.com  doug beck 

One detail is working against you: the NuBus clock rate is 10 Mhz.  To 
make it even worse, the 68020 has to synch with the NuBus -- this costs 
even more time.  I was told that the cost of synch'ing was about 200 ns, 
making the total cost at least 300 ns (this is from memory and so is 
probably not exact).  Don't forget that the video memory is also written 
across the same bus, so if there are screen updates you're bound to have 
some contention.

Wish I had better news ... :-)

mike (carlton@ji   ...!ucbvax!ji!carlton)